Glass sheet strip annealing method

ABSTRACT

A glass sheet strip annealing method utilizes a housing (18) along which a conveyor (26) including a gas support (28) supports a glass sheet strip G by pressurized gas for movement between entry and exit ends (22,24) of the housing before a conveyor drive (32) engages the strip after the surfaces thereof are cooled below the strain point. Best results are achieved when the glass sheet strip is supported only by the gas support (28) until its surfaces are placed in compression. Lower and upper manifolds (34,36) respectively support and convey the glass sheet strip within the housing (18) preferably by a recirculating gas flow supplied by gas burner (76) and associated gas jet pumps (78).

This is a divisional of application Ser. No. 08/383,602 filed on Jan.31, 1995, now U.S. Pat. No. 5,700,306, which is a continuation ofapplication Ser. No. 08/212,556, now abandoned, filed on Mar. 11, 1994as a continuation of application Ser. No. 07/992,169, now abandoned,filed on Dec. 17, 1992 as a continuation of application Ser. No.07/671,505, filed on Mar. 19, 1991 and issued on May 11, 1993 as U.S.Pat. No. 5,209,767.

TECHNICAL FIELD

This invention relates to an annealing lehr for annealing a glass sheetstrip.

BACKGROUND ART

Glass sheets are conventionally made by forming a continuous glass sheetstrip that is slowly cooled in an annealing lehr to provide annealing soas not to generate internal stresses that are so great as to prevent thestrip from subsequently being cut into sheets of a discrete length.Conventional processing forms the glass sheet while floating on a moltenmetal bath of tin and then delivers the glass sheet from the tin bath tothe annealing lehr for the slow cooling. Prior to entering the annealinglehr, the lateral edge portions of the glass sheet can be trimmed in ahot condition as disclosed by U.S. Pat. No. 4,749,400 Mouly et al.During the annealing, the temperature of the glass sheet strip is slowlycooled from the "annealing point" which is normally in the range ofabout 1000 to 1040° Fahrenheit (about 538 to 560° centigrade) to thestrain point which is generally in the range of about 925 to 970°Fahrenheit (about 495 to 520° centigrade). Between 925 and 1040°Fahrenheit (496 to 560° centigrade) is conventionally referred to as the"annealing range". More specifically, both the annealing point and thestrain point between which the annealing range extends are defined astemperatures that correspond either to a specific rate of elongation ofa glass fiber when measured by ASTM Method C336 or a specific rate ofmidpoint deflection of a glass beam when measured by ASTM Method C598.Internal stresses of a glass sheet at the annealing point aresubstantially relieved in minutes, while internal stresses at the strainpoint are substantially relieved in hours.

During conventional annealing, the continuous glass sheet strip issupported on conveyor rolls for conveyance from the annealing point tothe strain point through the annealing range. Since the glass isrelatively soft at the annealing point, its surfaces can be deformed byengagement with the conveyor rolls and thereby adversely affect opticalquality and mechanical strength.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an improved method forannealing a hot glass sheet strip without engaging the strip during slowcooling during the annealing range so as to provide good optical qualityand mechanical strength to the annealed glass.

In carrying out the above object and other objects of the invention, aglass sheet strip annealing method in accordance with the presentinvention utilizes a housing defining a heating chamber and having anentry end for receiving a continuous hot glass sheet strip just afterforming of the strip prior to cooling below the annealing point. Thehousing also has an exit end from which the strip exits the heatingchamber. Within the housing, the heating chamber has a decreasingtemperature from the entry end of the housing toward the exit endthereof to provide relatively slow cooling that anneals the strip. Aconveyor of the annealing lehr includes a gas support that deliversupwardly directed pressurized gas to provide the sole support of theglass sheet strip within the housing until the surfaces of the strip arecooled below the strain point. The conveyor also includes a drive forengaging the strip after the surfaces thereof are cooled below thestrain point to pull the strip from the entry end of the housing towardthe exit end thereof over the gas support.

In the preferred construction of the annealing lehr, the gas support ofthe conveyor provides the sole support for the glass sheet strip untilthe surfaces of the strip are placed in compression by the cooling whichnormally takes place as the center of the continuous glass sheet stripbegins to cool at a faster rate than the surfaces as the glassapproaches ambient temperature.

The preferred construction of the glass sheet strip annealing lehr hasthe gas support of the conveyor constructed to include a lower manifoldto which the pressurized gas is fed for upward flow that impinges withthe glass sheet strip to provide the support of the strip, and the gassupport of the conveyor also includes an upper manifold to which gas isfed for downward flow that impinges with the glass sheet strip tocooperate with the upward gas flow in providing uniform forcedconvection heat transfer with the lower and upper surfaces of the strip.Each of the lower and upper manifolds includes supply openings throughwhich the pressurized gas is fed for impingement with the glass sheetstrip, and each manifold also includes exhaust openings through whichthe gas is exhausted after impingement with the glass sheet strip. Eachmanifold has the supply and exhaust openings thereof provided withelongated shapes that extend transversely to the direction of movementof the glass sheet strip. These supply and exhaust openings of eachmanifold are in an alternating relationship along the direction ofmovement of the glass sheet strip.

In each of two preferred embodiments disclosed, each manifold isconstruction with each elongated exhaust opening having opposite endsand a central portion between the opposite ends and with the oppositeends of each exhaust opening having a progressively increasing flow areain a direction toward the central portion thereof to prevent a gaspressure buildup at the center of the strip. Both of the preferredembodiments have the supply openings thereof inclined so as to providedriving of the glass sheet strip by the pressurized gas flow toward theexit end of the housing. Between the entry and exit ends of the housing,the conveyor preferably includes a plurality of sets of the lower andupper manifolds that provide the forced convection cooling of the glasssheet strip.

In one preferred embodiment, each manifold of the annealing lehr ismolded from refractory material and preferably includes a cast platenhaving a surface that defines the supply and exhaust openings which haveelongated shapes that extend transversely to the direction of movementof the glass sheet strip and are arranged in an alternating relationshipwith respect to each other. Each manifold also includes a cast manifoldmember that feeds the pressurized gas to the supply openings of theplaten and receives the gas from the exhaust openings of the platen forrecirculating flow back to the supply openings. Each manifold preferablyfurther includes a gas burner and at least one gas jet pump mounted bythe manifold member to receive pressurized and heated products ofcombustion from the gas burner for mixing with the gas returned from theexhaust openings for recirculating flow back to the supply openings.

In the preferred construction of the refractory molded manifold whichincludes the cast platen as well as the cast manifold member, themanifold member includes two pairs of spaced side walls with each pairof spaced side walls defining a return passage for receiving gas fromthe exhaust openings of the platen. A plurality of the gas jet pumps aremounted on each pair of side walls and function to mix the pressurizedand heated products of combustion received from the gas burner with thegas returned from the exhaust openings of the platen for therecirculating flow back to the supply openings of the platen. The twopairs of spaced side walls are spaced from each other to define a mixingplenum in which the pressurized gas is received from opposite directionsfrom the gas jet pumps for mixing prior to being fed to the supplyopenings of the platen.

Each manifold member of the refractory embodiment of the manifold alsopreferably includes temperature controllers for controlling thetemperature of the pressurized gas delivered from the mixing plenum tothe supply openings of the platen. These temperature controllers eachinclude an electric resistance element to which a voltage is applied asneeded to provide the proper degree of additional heating for heatingthe gas that provides the forced convection heating upon being deliveredto the supply openings of the platen.

Each manifold member of the refractory embodiment of the manifold alsoincludes vertical walls spaced along the direction of movement of theglass sheet strip to divide the mixing plenum with one temperaturecontroller and a pair of oppositely directed gas jet pumps locatedbetween each pair of vertical walls. The pair of oppositely directed gasjet pumps that feed pressurized gas between each pair of vertical wallsof the manifold member are located at different elevations to provide acircular mixing flow. This circular mixing flow takes place away fromthe temperature controller with respect to the plane of strip conveyanceat a location between the two vertical walls involved.

In another preferred embodiment disclosed, each manifold is fabricatedfrom sheet metal as opposed to being molded from refractory material.

The conveyor drive of the annealing lehr as disclosed includes a rollerthat engages the lower surface of the glass sheet strip to pull thestrip from the entry end of the housing toward the exit end thereof overthe gas support. Thus, in the preferred construction, the roller of thedrive pulls the glass sheet strip between the lower and upper manifoldsof the gas support whose forced convection with the lower and uppersurfaces provides the slow cooling of the strip for the annealing.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a somewhat schematic side elevational view of a glass sheetstrip annealing lehr constructed in accordance with the presentinvention;

FIG. 2 is a partially broken away perspective view of an entry end of ahousing of the annealing lehr;

FIG. 3 is a cross-sectional view of the annealing lehr taken generallyalong the direction of line 3--3 in FIG. 1;

FIG. 4 is a side elevational view of the annealing lehr taken along thedirection of line 4--4 in FIG. 3;

FIG. 5 is a partially broken away perspective view of a platen of amanifold of the annealing lehr through which pressurized gas is fed forrecirculating flow to support and slowly cool the glass sheet stripduring the annealing;

FIG. 6 is a plan view of the platen taken along the direction of line6--6 in FIG. 3 and illustrates the construction of supply and exhaustopenings through which the pressurized gas is fed for recirculatingflow;

FIG. 7 is a sectional view taken along the direction of line 7--7 inFIG. 3 through lower and upper platens of lower and upper manifolds andillustrates the way in which the pressurized gas is recirculated forimpingement with the glass sheet strip; and

FIG. 8 is a perspective view illustrating another embodiment of themanifold.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 of the drawings, the method of the invention isperformed by a glass sheet forming system that is generally indicated by10 and includes a forming station 12 at which a continuous hot glasssheet strip G is formed, a trimming station 14 at which the lateral edgeportions of the hot glass sheet strip are trimmed, and an annealing lehr16 that is constructed in accordance with the present invention toprovide annealing of the glass sheet strip prior to cutting of the stripinto glass sheets of discrete lengths. The forming station 12 may be ofany conventional construction but normally will provide forming of thehot glass sheet strip G by floating thereof on a bath 13 of molten metalthat conventionally is hot tin. After horizontally leaving the formingstation 12, the glass sheet strip G passes through the trimming station14 as mentioned above where its lateral edge portions may be trimmed toremove any edge irregularities present prior to entering the annealinglehr 16 for annealing. However, it should be mentioned that any type offorming of the glass sheet strip G can be utilized and that it is notabsolutely necessary for edge trimming to be performed prior to deliveryof the glass sheet strip to the annealing lehr 16 of the presentinvention for the slow cooling that provides annealing.

With continuing reference to FIG. 1, the glass sheet strip annealinglehr 16 of this invention includes a housing 18 defining a heatingchamber 20 and has an entry end 22 for receiving the continuous hotglass sheet strip G which is moved horizontally into the heating chamberjust after forming of the strip. The housing 18 also has an exit end 24from which the glass sheet strip exits the heating chamber 20. Along thelength of the housing 18, the heating chamber 20 has a decreasingtemperature from the entry end 22 of the housing toward the exit end 24of the housing to provide relatively slow cooling that anneals the glasssheet strip G.

As best illustrated by combined reference to FIGS. 1 and 3, a conveyor26 of the annealing lehr includes a gas support 28 that deliversupwardly directed pressurized gas as illustrated by arrows 30 in FIG. 7.This upwardly directed pressurized gas provides the sole support of theglass sheet strip within the annealing lehr housing 18 shown in FIG. 1until the surfaces of the strip are cooled below the strain point. Adrive 32 of the conveyor 26 engages the glass sheet strip G as shown inFIG. 1 after the surfaces thereof are cooled below the strain point andpulls the strip from the entry end 22 of the housing toward the exit end24 thereof over the gas support 28. As such, the surfaces of the glasssheet strip G are not mechanically engaged during the annealing withinthe annealing lehr housing 18 in order to preserve optical qualities ofthe glass sheets that are ultimately cut from the continuous strip.

Best results are achieved when the gas support 28 provides the solesupport for the glass sheet strip G until the surfaces of the glasssheet strip are placed in compression by the cooling. More specifically,this compression of the surfaces is generated after the glass sheetstrip has been cooled sufficiently so that the temperature gradientbetween its surfaces and its center begins to disappear as the coolingslows at ambient temperature. The drive 32 then engages the glass sheetstrip after the surfaces thereof are placed in compression by thecooling to pull the strip from the entry end 22 of the housing 18 towardthe exit end 24 thereof over the gas support 28 of conveyor 26.

As illustrated by combined reference to FIGS. 1 and 3, the gas support28 of the conveyor 26 preferably includes a lower manifold 34 to whichthe pressurized gas is fed for upward flow that impinges with the glasssheet strip G to provide the support of the strip as illustrated byarrows 30 in FIG. 7. Furthermore, the gas support 28 illustrated inFIGS. 1 and 3 also includes an upper manifold 36 to which gas is fed fordownwardly directed flow that impinges with the glass sheet strip G asillustrated by arrows 38 in FIG. 7 to cooperate with the upward gas flowin providing uniform forced convection heat transfer with the lower andupper surfaces of the glass sheet strip G.

As illustrated by combined reference to FIGS. 1 and 7, each of the lowerand upper manifolds 34 and 36 includes supply openings 40 through whichthe pressurized gas is fed for impingement with the glass sheet strip G.Each of the lower and upper manifolds 34 and 36 also includes exhaustopenings 42 through which the gas is exhausted after impingement withthe glass sheet strip G as illustrated in FIG. 7 by arrows 44 and 46respectively associated with the lower and upper manifolds. Each of themanifolds as shown in FIG. 6 has a horizontally extending planar surface48 at which the supply and exhaust openings are defined. These supplyand exhaust openings 40 and 42 preferably have elongated slit shapesthat extend transversely with respect to the direction of movement ofthe glass sheet strip as identified by arrow 50. Supply and exhaustopenings 40 and 42 of each manifold are in an alternating relationshipalong the direction of movement of the glass sheet strip so as to permita recirculating flow of gas as is hereinafter more fully described. Eachelongated exhaust opening 42 has opposite ends 52 and a central portion54 between the opposite ends. These exhaust openings 42 each have aprogressively increasing flow area in a direction from its ends 52toward the central portion 54 thereof to prevent a gas pressure buildupat the center of the glass sheet strip. More specifically, asillustrated, the exhaust openings 42 have an increasing width from theends 52 toward the central portion 54 to prevent the gas pressurebuildup at the center of the glass sheet strip which is adjacent thecentral portion 54 of the exhaust openings.

As shown best by FIG. 7, each of the lower and upper manifolds 34 and 36has supply passages 56 that are inclined and feed the supply openings 40so as to provide driving of the glass sheet strip by the pressurized gasflow toward the exit end of the housing. This driving takes place byproviding the inclination to the upward and downward gas flowsidentified by arrows 30 and 36 such that these gas flows tend to movethe glass sheet G in the direction of arrow 50 which is toward the exitend of the housing.

As illustrated in FIG. 1, the conveyor 26 preferably includes aplurality of sets of the lower and upper manifolds 34 and 36 between theentry and exit ends 22 and 24 of the housing 18 of the annealing lehr16. More specifically, five sets of the lower and upper manifolds 34 and36 are illustrated; however, a greater or less number of the manifoldsets can be utilized depending upon sizing and the processing parametersdesired.

As shown in FIG. 3, each of the lower and upper manifolds 34 and 36 ismolded from a suitable refractory material such as sinter bonded fusedsilica so as to have good resistance to thermal warpage. Morespecifically, each manifold includes a cast platen 60 that defines thesurface 48 in which the supply and exhaust openings are located with theconstructions previously described. Each platen 60 also has a surface 62that extends parallel to its planar surface 48 and defines elongatedplenum portions 64 extending therefrom with an initially convergingshape to feed the supply passages 56 that feed the pressurized gas tothe supply openings 40 as previously described. Each plenum 60 alsoincludes elongated exhaust chambers 66 that receive gas from the exhaustpassages 58 and have opposite ends that are communicated with associatedreturn passages 68 shown in FIG. 5. An associated end wall 70 isolateseach return passage 68 from the adjacent plenum portion 64 whileproviding the communication thereof with the exhaust chambers 66 so asto permit recirculating flow of the gas as is hereinafter more fullydescribed.

As also illustrated in FIG. 3, each of the lower and upper manifolds 34and 36 also includes a cast manifold member 72 that feeds thepressurized gas to the supply openings of the associated platen 60 andreceives the gas from the exhaust openings of the platen forrecirculating flow back to the supply openings. These manifolds 72 arerespectively located below and above the platen 60 of the lower andupper manifolds and are secured thereto by associated bolt-typefasteners 74.

As also shown in FIG. 3, each of the lower and upper manifolds 34 and 36additionally includes a gas burner 76 and at least one gas jet pump 78mounted by the manifold member 72. In the preferred constructiondisclosed, there are a plurality of gas jet pumps 78 mounted by eachmanifold member 72, specifically nine each side thereof, and asillustrated in FIG. 4 these gas jet pumps are located in a staggeredarray of lower and upper sets. Each of these gas jet pumps is connectedby feeder conduits 80 fed by an associated main conduit 82 from a mixingchamber 84 to which the heated products of combustion are fed from theassociated gas burner 76. These heated products of combustion are fed tothe gas jet pumps 78 for flow through a restricted nozzle 86 to providea primary gas flow 88 that induces a secondary flow 90 of the return gasreceived from the exhaust openings of the associated platen 60 forrecirculating flow of the mixed gas as shown by arrows 92 back to thesupply openings. Delivery members 94 feed the mixed flow back to thesupply openings as is hereinafter more fully described.

As best illustrated in FIG. 3, each manifold member 72 includes twopairs of spaced outer and inner side walls 96 and 98 that extendgenerally vertically from a horizontal wall 100 to the associated platen60. Each pair of outer and inner spaced side walls 96 and 98 defines areturn passage 102 for receiving gas from the exhaust openings of theplaten via the return passages 68 previously described in connectionwith FIG. 5. As previously mentioned in connection with FIGS. 3 and 4, aplurality of the gas jet pumps 78 are associated with each manifold 34and 36 and are mounted on each pair of spaced side walls 96 and 98thereof in staggered lower and upper sets. These gas jet pumps as wasalso previously mentioned, function to mix the pressurized and heatedproducts of combustion received from the gas burner 76 through thefeeder and main conduits 80 and 82 and the mixing chamber 84 so as tomix with the gas returned from the exhaust openings of the associatedplaten 60 for recirculating flow back to the supply openings of theplaten. The two pairs of spaced side walls 96 and 98 are also spacedfrom each other to cooperate with each other and with the horizontalwall 100 thereof as well as the surface 62 of the associated platen todefine a mixing plenum 104 in which the pressurized gas is received fromopposite directions from the gas jet pumps for mixing prior to being fedto the supply openings of the platen as previously described inconnection with FIG. 7. This mixing chamber 104 is divided by verticalwalls 105 spaced as shown in FIG. 2 along the length of the lehr alongwhich the glass sheet strip is moved. A pair of the gas jet pumps 78feed pressurized gas between each pair of vertical walls 105 fromopposite directions at upper and lower positions that alternate alongthe direction of the glass sheet strip movement. Such a constructionprovide a circular mixing as shown by arrows 103 in FIG. 3 to therebyprovide pressure and temperature uniformity. Any variation in the gasdelivery pressure and temperature over the lateral width of themanifolds due to the upper and lower locations of the two gas jet pumps78 that feed between each pair of vertical walls 105 is accommodated forby the alternating relationship of these positions along the directionof movement of the glass sheet strip. Furthermore, pressure variationsalong the lateral width are the same both above and below the glasssheet strip G in order to maintain planarity.

As illustrated in FIGS. 2 through 4, each manifold member 72 alsoincludes temperature controllers 106 for controlling the temperature ofthe pressurized gas delivered from the mixing chamber to the supplyopenings of the associated platen 60. More specifically, eachtemperature controller 106 as shown in FIG. 2 includes an electricresistance element 108 to which a voltage is applied as needed toprovide the appropriate temperature at the particular location involvedso as to provide the proper degree of heating at that location of theannealing lehr. These temperature controllers 106 are mounted betweenvertical walls 105 by the spaced side walls 96 and 98 of the associatedmanifold member 72 toward the glass sheet strip from the gas jet pumps78 such that all of the gas delivered from the gas jet pumps must passby the temperature controllers and thus be heated thereby so as toprovide the proper temperature of the pressurized gas delivered to thesupply openings. One temperature controller 106 and two gas jet pumps 78are mounted between each pair of vertical walls 105 of the manifoldmember 72. The good temperature control achieved with the lehr allowsnonlinear cooling that can decrease the time needed to perform theannealing. For example, after the glass sheet strip is cooled below thestrain point, holding its temperature for a minute or slightly longer atabout 545° centigrade allows subsequent cooling at a faster rate to 480°centigrade, without inducing temporary internal stresses that wouldfracture the glass without the pause in cooling, while providing anoverall faster cooling time. Likewise, other nonlinear cooling curvescan be utilized due to the good temperature control achieved.

With the embodiment of FIGS. 2 through 7, the glass sheet strip G isfloated by the pressurized gas above the planar surface 48 of each lowermanifold 34 a very small distance, such as about 1 to 2 millimeters, andis spaced below the planar surface 48 of each upper manifold 36 by adistance that is normally greater than the lower spacing such as two toseveral times the lower spacing. The extent of each spacing for bestresults depends upon glass thickness, the speed of conveyance, thetemperature involved and other operating parameters.

With reference to FIG. 8, another construction for the lower and uppermanifolds is illustrated by the one lower manifold 34' shown by solidline representation. This manifold is fabricated from sheet metal asopposed to being molded from refractory material like the previouslydescribed embodiment and is utilized with a plurality of like lowermanifolds 34' and, preferably, with a plurality of like upper manifolds36' as shown by phantom line representation so that the glass sheetstrip can be conveyed therebetween in a generally similar manner to thepreviously described embodiment. The manifold 34' has a gas supplyopening 40' of an elongated shape that extends transversely to thedirection of movement of the glass sheet strip as with the previouslydescribed embodiment. At its downstream side, the lower manifold 34' hasa construction for cooperating with the planar upstream side of theadjacent lower manifold 34' to define an exhaust openings 42' of anelongated shape that receives the gas after impingement with the glasssheet strip. This exhaust opening has opposite ends 52' and a centralportion 54'. As with the previously described embodiment, the elongatedgas exhaust opening 42' has a progressively increasing flow area in adirection toward the central portion 54' thereof from its opposite ends52' so as to prevent a gas pressure buildup at the center of theconveyed glass sheet strip. While this progressively increasing flowarea in the previously described embodiment is provided by an increasingwidth of the exhaust opening, the fabricated sheet metal embodiment ofthe manifold 34' provides the increasing flow area by a progressivelyincreasing depth of the exhaust opening 42' from its ends 52' toward itscentral portion 54'. Hot pressurized gas such as from the products ofcombustion of an associated gas burner are fed into side inlets 110 forflow to the supply openings 40' preferably through supply passages 56'that are inclined like with the previously described embodiment.

As illustrated in FIG. 1, the conveyor drive 32 of the annealing lehr 16includes at least one roller 112 that engages the lower surface of theglass sheet strip G to pull the strip from the entry end 22 of thehousing 18 toward the exit end 24 thereof over the gas support 28provided by the gas manifolds as previously described. Normally, theroller drive 32 will also include other rollers of a conveyor on whichfinal cooling takes place.

As best illustrated in FIG. 3, the annealing lehr includes a frameworkgenerally designated by 114 for supporting the components of the housing18. This housing framework 114 includes vertical legs 116 and horizontalbeams 118 that extend between and are supported by the legs. Each lowermanifold 34 has four associated lower jacks 120 whose lower ends aresupported by an associated horizontal beam 118 and whose upper endssupport the adjacent corner of the manifold member 72. These jacks 120extend through an insulated floor 122 of the housing 18 just inward frominsulated lower side walls 124 of the housing. Upper vertical jacks 126of the framework 114 have lower ends supported by adjacent horizontalbeams 118 and have vertically movable carriages 128 that are connectedas shown in FIG. 2 by coupling shafts 130 along the longitudinal lengthof the housing. These carriages 128 are connected by longitudinallyextending beams 132 shown in FIG. 3 and support an insulated ceiling 134and insulated upper side walls 136 for vertical movement as the jackcarriages 128 are adjusted. Suspension rods 138 and 140 support eachupper manifold 36. More specifically, four of the suspension rods 138have upper ends supported by the insulated ceiling 134 and have lowerends that support the four corners of the platen 60 of the uppermanifold 36. Likewise, four of the suspension rods 140 have upper endsalso supported by the insulated ceiling 134 and have lower ends thatsupport the four corners of the manifold member 72 of the associatedupper manifold 36. The upper and lower ends of these suspension rods 138and 140 have threaded connections that provide securement so that theupper platen 60 is level, while vertical adjustment of the carriages 128as previously described spaces the upper platen 60 at the appropriateelevation with respect to the lower platen 60 whose elevation iscontrolled by the lower jacks 120 as previously described.

As shown in FIGS. 1 and 2, vertically movable doors 142 that arepreferably constructed of ceramic material such as by molding fromsinter bonded fused silica particles are located at each side of theupper platen 60. A pair of chains 144 are connected to the doors 142 andextend over pulleys 146 mounted on the horizontally extending beams 132in a suitable manner, and from the pulleys the chains 144 extenddownwardly to a horizontal handle 148 that is movable downwardly to thuspull the door 142 upwardly and permit viewing of the glass sheet stripat the adjacent location.

As shown in FIG. 2 and schematically in FIG. 4, windows 150 are locatedbetween the adjacent upper manifolds 36 to permit viewing of theconveyed glass sheet strip in addition to the viewing permitted by theopening of the doors 142 as previously described in connection withFIGS. 2 and 3.

As shown in FIGS. 2 through 4, a cullet door mechanism 152 is located atone side of the housing 18 and controls positioning of a lower culletdoor 154 between a horizontal closed position that maintains thepressurized atmosphere within the lehr housing 18 and a vertical openposition that permits cullet to fall downwardly when the glass sheetstrip is broken.

As illustrated in FIGS. 2 and 4, start-up rolls 156 are located betweenalternate sets of the lower and upper manifolds and normally positionedduring steady state operation below the glass sheet strip by associatedpositioning and drive mechanisms 158. During start-up operation, thesemechanisms 158 raise the start-up rolls 156 to initially convey theglass sheet strip G through the annealing layer in order to facilitatereaching the steady state operation as previously described. Betweeneach adjacent pair of start-up roll drive mechanisms 158, the annealinglayer includes a pyrometer assembly 160 for measuring the temperatureprofile of the glass sheet strip along its lateral width during theconveyance.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

What is claimed is:
 1. A glass sheet strip annealing method,comprising;forming a continuous hot glass sheet strip by floatingthereof on a bath of hot molten tin and then moving the striphorizontally therefrom; horizontally moving the newly formed continuoushot glass sheet strip with a temperature above the annealing point ofthe glass sheet strip into an entry end of a heated chamber that has adecreasing temperature from the entry end toward an exit end; supportingthe newly formed glass sheet strip within the heated chamber on upwardlydirected pressurized gas to provide the sole support of the glass sheetstrip until the surfaces of the strip are cooled below the strain pointof the glass sheet strip; impinging pressurized gas upon the glass sheetstrip from above within the heated chamber to cooperate with theupwardly directed pressurized gas in cooling the glass sheet strip;drivingly engaging the surfaces of the glass sheet strip after thesurfaces have cooled below the strain point of the glass sheet strip,the driving engagement of the surfaces pulling the strip from the entryend of the heated chamber toward the exit end thereof over the upwardlydirected pressurized gas; and wherein the pressurized gas isrecirculated and mixed with heated products of combustion for flow backto the strip, the mixing providing pressure and temperature uniformityto the pressurized gas.
 2. A glass sheet strip annealing method as inclaim 1 wherein the glass sheet strip is drivingly engaged after thecooling has proceeded sufficiently so the surfaces of the glass sheetstrip are in compression.
 3. A glass sheet strip annealing method as inclaim 1 wherein the upwardly directed pressurized gas is exhaustedtoward the center of the glass sheet strip to prevent a gas pressurebuildup at the center of the strip.
 4. A glass sheet strip annealingmethod as in claim 1 wherein the heated products of combustion and therecirculated gas are mixed by circular mixing.
 5. A glass sheet stripannealing method as in claim 4 wherein said circular mixing is providedby feeding the heated products of combustion and the recirculated gasthrough a pair of oppositely directed gas jet pumps located at differentelevations.
 6. A glass sheet strip annealing method, comprising:forminga continuous hot glass sheet strip by floating thereof on a bath of hotmolten tin and then moving the strip horizontally therefrom;horizontally moving the newly formed continuous hot glass sheet stripwith a temperature above the annealing point of the glass sheet stripinto an entry end of a heated chamber that has a decreasing temperaturefrom the entry end toward an exit end; supporting the newly formed glasssheet strip within the heated chamber on upwardly directed pressurizedgas that is recirculated and mixed with heated products of combustionand that provides the sole support of the glass sheet strip until thesurfaces of the strip are placed in compression; impinging furtherpressurized gas upon the glass sheet strip from above within the heatedchamber to cooperate with the upwardly directed pressurized gas incooling the glass sheet strip, and recirculating and mixing said furtherpressurized gas with heated products of combustion; and drivinglyengaging the surfaces of the glass sheet strip after cooling hasproceeded sufficiently so the surfaces are in compression, the drivingengagement of the surfaces pulling the strip from the entry end of theheated chamber toward the exit end thereof through the pressurized gas.